82 ME. C. W. ANDEEWS ON THE SKULL AND 



of the hypotarsus. Lower down the shaft it is narrowed and flattened, its outer 

 border being formed by a prominent ridge, which is continued upward and outward, 

 and terminates above in the process which forms the outer border of the external 

 o-lenoid fossa ; its inner border is formed by a less prominent ridge, which is not, as in 

 Cariama, continuous above with the inner ridge of the hypotarsus. 



The outer face of the shaft is bordered by the ridges which form the outer edges 

 of the anterior and posterior faces. This surface widens out towards the middle of 

 the bone, and is flat or even slightly concave. The outer surface is slightly convex, 

 and is not very sharply marked off from the posterior surface. 



As above mentioned, the shaft is incomplete in both the metatarsi of the type- 

 skeleton, but the distal portion (three or four inches) of the right metatarsus is very well 

 preserved. The upper portion of the shaft preserved in this specimen is very slender 

 and roughly triangular in section, one angle of the triangle being a rugose ridge on 

 the posterior surface. A short distance above the inner trochlea, and at the lower 

 end of the ridge just mentioned, is the surface for the attachment of the hallux (hal.). 

 Below this the posterior surface is slightly concave from side to side. The anterior 

 surface has near its outer side a shallow groove deepening distally and having at its 

 lower end the foramen for the tendon of the adductor digiti externi. This foramen 

 leads into two channels, one opening between the outer and middle trochlea, the other 

 on the posterior surface of the bone immediately above the trochlese. 



The distal trochlese are arranged in a slightly curved line (fig. 17). The median 

 trochlea (tr. 3) is very large and its articular surface is sharply delimited, both 

 anteriorly and posteriorly ; the median groove is much deeper behind than in front. 

 The inner trochlea (tr. 2) is relatively small, and is considerably shorter than the 

 middle one. Its articular surface is evenly convex from side to side, except on its 

 posterior side, where it is slightly grooved. It is situated a little posterior to the 

 middle trochlea, behind which it projects considerably. The outer trochlea (tr. 4) is 

 rather larger than the inner and is slightly longer ; it also projects considerably 

 behind the median, and its articular surface is grooved posteriorly only. The lateral 

 surfaces of all the trochlese are deeply excavated by pits for the insertion of the 

 ligaments of the toes. 



In comparing the metatarsus of Phororhacos with that of other birds, it must be 

 remembered that it has probably been profoundly modified in correlation with the 

 loss of the power of flight and the consequently exclusively pedestrian progression 

 of the bird. Among the peculiarities which may probably be thus accounted for 

 are the simple hypotarsus, the relatively great length of the bone, and the disposition 

 of the distal trochlese. 



The metatarsus of Diomedea differs in several respects, the chief of which are 

 complete absence of all trace of a hind toe, relatively large size of the articular ends 

 compared with the shaft, breadth and complication of the hypotarsus, and absence of 

 a pit for ligament at the outer side of the base of the intercondylar tuberosity. 



